ACT science practice test 18

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


An experiment is set up to look at the physics of bouncing a ball, as shown in Figure 1.

Figure 1

When the ball is dropped, its initial velocity is 0 m/s. Velocity will increase until impact with the ground, at which point the ball's velocity immediately drops to 0 m/s again. After impact, velocity almost immediately increases to maximum post-impact velocity, and then begins to fall again as gravity works against it, slowing it down. The ball's velocity returns to 0 m/s when the ball is at its apex, or highest vertical point, post impact.

When a ball bounces, it deforms and becomes flatter. This is called elasticity. The more elasticity a material has, the better it is able to act like a spring and absorb force by being compressed, then use this force to "spring" back into the air. Post-impact velocity and the amount of time between velocity of 0 m/s at impact and velocity of 0 m/s at post-impact apex are affected by elasticity. Figure 2 shows the velocity of a ball versus time for balls with various elasticities and weights dropped from 1 meter height. Because gravity causes all objects to fall at the same speed regardless of weight, pre-impact velocities are identical for all balls.

Figure 2

1. Based on the data in Figure 2, the maximum post-impact velocity of a ball will be smallest if the elasticity of the ball is:

F. 1.5 Pa.
G. between 1 and 1.5 Pa.
H. between 0.5 and 1 Pa.
J. 0.5 Pa.

2. Based on the information in Figure 2, a ball being dropped from 1 meter height with an elasticity of 0.2 Pa and a weight of 0.5 kg would have a maximum post-impact velocity of:

A. less than 0.50 m/s.
B. 0.75 m/s.
C. 1.0 m/s.
D. greater than 1.25 m/s.

3. Consider a ball as it completes one bounce, from drop to post-impact apex. If this ball has a weight of 2 kg and an elasticity of 0.50 Pa, based on the data in Figure 2, how many times does the ball have a velocity of 1.00 m/s ?

F. One time
G. Two times
H. Three times
J. Four times

4. Based on the data in Figure 2, how does the velocity of a ball change as it goes from impact to apex?

Drop to Impact

A. Increases only
B. Decreases only
C. Increases then decreases
D. Decreases then increases

5. A ball will deform permanently and not spring back off the ground if the velocity with which it hits the ground exceeds the ball's elastic limit. Based on the data in Figure 2, if a ball is dropped from one meter and has a weight of 3 kg, an elasticity of 0.8 Pa, and an elastic limit of 2.75 m/s, will the ball deform permanently?

F. Yes, because the velocity with which the ball hits the ground is less than its elastic limit.
G. Yes, because the velocity with which the ball hits the ground is greater than its elastic limit.
H. No, because the velocity with which the ball hits the ground is less than its elastic limit.
J. No, because the velocity with which the ball hits the ground is greater than its elastic limit.

A group of students studied the frictional forces involved on stationary objects.

In a series of experiments, the students used rectangular shaped objects of various materials that all had identical masses. One end of a plastic board coated with a polymer film was fastened to a table surface by a hinge so the angle θ between the board and table could be changed, as shown in Figure 1.

Objects were placed on the opposite end of the board, and the angle θ at which the object started to slide was recorded. The tangent of this angle represents the coefficient of static friction between the object and the polymer surface. This coefficient is proportional to the force required to move a stationary object. Higher coefficients mean that greater forces of friction must be overcome to initiate movement.

The dimensions of the objects gave them 3 distinct faces of unequal area as shown in Figure 2. Unless otherwise stated, the objects were placed on the ramp with Face A down.

Experiment 1

Four objects made of different materials were placed on the ramp at a temperature of 25°C. The ramp was gradually raised and as soon as the object started to move, the angle θ of the ramp was recorded in Table 1.

Table 1
Object materialθ (degrees)
Granite12.1
Copper16.8
Wood22.0
Brick31.1

Experiment 2

The procedure for Experiment 1 was repeated with the wooden object, varying which face was placed down on the ramp. Results were recorded in Table 2.

Table 2
Faceθ (degrees)
A22.0
B22.0
C22.0

Experiment 3

The procedure for Experiment 1 was repeated with the wooden object, varying the temperature of the polymer ramp. Results for 5 temperatures were recorded in Table 3.

Table 3
Temperature (°C)θ (degrees)
018.5
2522.0
5025.4
7529.0
10032.5

Experiment 4

The procedure for Experiment 1 was repeated with multiple wooden objects. For each trial, the objects were stacked on top of each other before raising the ramp. The angle θ where the stack started to slide was recorded in Table 4.

Table 4
Number of objectsθ (degrees)
222.0
322.0
422.0

6. If the procedure used in Experiment 3 had been repeated at a temperature of 62.5°C, the angle required for the object to start moving down the ramp most likely would have been closest to which of the following?

A. 27.2 degrees
B. 29.2 degrees
C. 30.3 degrees
D. 31.4 degrees

7. Suppose the students had placed the 4 objects used in Experiment 1 on the ramp when it was flat and pushed each of the objects, such that the amount of force applied to each object gradually increased until it moved. Based on the results of Experiment 1, the object made of which material would most likely have taken the greatest amount of force to start moving?

F. Brick
G. Wood
H. Copper
J. Granite

8. Based on the results of Experiments 1 and 4, what was the effect, if any, of the weight of the object on the coefficient of static friction?

A. The coefficient of static friction always increased as the object's weight increased.
B. The coefficient of static friction always decreased as the object's weight increased.
C. The coefficient of static friction increased and then decreased as the object's weight increased.
D. The coefficient of static friction was not affected by the weight of the object.

9. In Experiment 1, the reason the students used objects made of different materials was most likely to vary the amount of frictional force between the:

F. plastic board and the polymer surface.
G. various objects and the polymer surface.
H. objects made of different materials when brought into contact with each other.
J. stacked objects, so that the objects would not fall over when the angle of the ramp was raised high enough to cause motion.

10. Which of the following ranks the different types of objects used, in order, from the material that presented the greatest resistance to movement to the material that presented the least resistance to movement?

A. Granite, copper, wood, brick
B. Copper, wood, granite, brick
C. Granite, wood, brick, copper
D. Brick, wood, copper, granite

11. The main purpose of Experiment 3 was to determine the effects of temperature on which of the following variables?

F. Coefficient of static friction between wood and wood
G. Coefficient of static friction between wood and polymer
H. Mass of the wooden object
J. Total frictional force of the polymer on all objects placed on the ramp